class Instrument:
    def play(self):
        pass
class Erhu(Instrument):
    def play(self):
        print('二胡在演奏')

class Piano(Instrument):
    def play(self):
        print('钢琴在演奏')

class Violin(Instrument):
    def play(self):
        print('小提琴在演奏')

#多态
def make_sound(object):
    object.play()

erhu=Erhu()
piano=Piano()
violin=Violin()

make_sound(erhu)
make_sound(piano)
make_sound(violin)